1. Field of the Invention
The present invention relates to a solid-state imaging device and a method for manufacturing the same, and to an electronic apparatus including the solid-state imaging device, such as a camera, and to a camera module.
2. Description of the Related Art
Solid-state imaging devices (image sensors) include CCD image sensors that include a charge-coupled device (CCD) for read-out signal charges, and CMOS image sensors in which each pixel includes one photoelectric conversion portion and a plurality of pixel transistors. These are used in a variety of portable terminal apparatuses, such as digital still cameras, digital video cameras, and cellular phones with a camera.
A CCD image sensor includes two-dimensionally arranged light-receiving portions acting as photoelectric conversion portions (photodiodes) that convert input light into signal charges and store the signal charges, and the stored signal charges are transferred through a vertical CCD register portion and a horizontal CCD register portion. In this type of solid-state imaging device, incoming light is reflected from the surface of the silicon substrate due to a difference in refractive index between the silicon oxide-based material of the gate insulating film, surface protective layer or planarizing layer and the silicon substrate. Consequently, the amount of light reaching the light-receiving portion is reduced and the sensitivity is reduced. Accordingly, the solid-state imaging device is provided with a silicon nitride antireflection layer over the light-receiving portion, and the multiple reflection effect is used to reduce the reflection of incoming light, thereby enhancing the sensitivity.
As the number of pixels in the solid-state imaging device is increased, the light-receiving area is reduced, and the opening width of the light-shielding film is reduced to a size less than or equal to the wavelength of light entering the photodiodes or the light-receiving portions. Consequently, incoming light is diffused to regions other than the light-receiving portion by diffraction. This can be a cause of the decrease in sensitivity and the occurrence of smears.
If the opening width of the light-shielding film is smaller than the wavelength of incoming light, the incoming light is diffused to regions other than the light-receiving portion by Fresnel diffraction. Consequently, charges generated in regions other than the light-receiving portion flow into the vertical CCD register portion to generate smears resulting in noises. Also, since the incoming light is diffused to regions other than the light-receiving portion, the sensitivity is reduced.
This phenomenon occurs not only in CCD image sensors, but also in CMOS image sensors, particularly, in a CMOS image sensor in which the charge storage portion is disposed at a side of the light-receiving portion so as to achieve a global shutter function. In CMOS image sensors having a global shutter function, the charge storage portion temporarily storing charges may be defined by a floating diffusion portion, or a memory portion disposed between the light-receiving portion and a floating diffusion portion. In these CMOS image sensors, if the opening width of the light-receiving portion is reduced to a size smaller than or equal to the wavelength of incoming light, the incoming light is diffused to regions other than the light-receiving portion, as described above, by diffraction. This can be a cause of the decrease in sensitivity and the occurrence of noise.
A CCD image sensor has been proposed in which the diffraction effect of incoming light is reduced by reversing the phase of incoming light at an open end of the light-receiving portion, in, for example, Japanese Unexamined Patent Application Publication Nos. 05-206425 and 2008-41847.
The structure for CMOS image sensors disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-95792 is well known, in which a forward tapered shape of a waveguide structure near the silicon substrate is changed into a reverse tapered shape for total reflection of light entering the light-receiving portion of the silicon substrate through the lower end of the waveguide so that the light collection efficiency is enhanced. Japanese Unexamined Patent Application Publication No. 2009-252949 discloses a structure for CMOS image sensors in which copper wiring and overlying wider diffusion-preventing metal wiring are formed by a damascene process as wiring over the semiconductor substrate with a photoelectric conversion portion acting as the light-receiving portion.